Characterization of benzimidazole and other oxidative and conjugative metabolites of brimonidinein vitroand in ratsin vivousing on-line H/D exchange LC-MS/MS and stable-isotope tracer techniques

作者：J. Ni, Josh Rowe, Todd M. Heidelbaugh, Sukesh Narayan Sinha, Andrew Acheampong · 发表于：Xenobiotica · 年份：2006 · DOI：10.1080/00498250601047897 · 被引用次数：20 · 研究领域：Synthesis and Biological Evaluation、Quinazolinone synthesis and applications、Phenothiazines and Benzothiazines Synthesis and Activities

The characterization of brimonidine metabolites presents some challenges since brimonidine and its metabolites generate few structurally informative fragment ions in the LC-MS/MS spectra. The objective of the current study is to use on-line hydrogen/deuterium (H/D) exchange LC-MS/MS and stable-isotope tracer techniques to further characterize unknown brimonidine metabolites in vitro and in vivo. Brimonidine and D4-brimonidine were co-incubated in rat and human microsomes and rabbit aldehyde oxidase in vitro. In addition, the urine was collected from rats co-administered orally with brimonidine and D4-brimonidine. The hepatic microsomal and urinary metabolites were then characterized by H/D LC-MS/MS system. In addition to previously characterized 2-oxobrimonidine, 3-oxobrimonidine and 2,3-dioxobrimonidine, the results show that oxidation occurs at quinoxaline ring producing oxo-hydroxybrimonidine and hydroxyquinoxaline metabolites. The hydroxyquinoxaline metabolite was only observed in microsomal incubations with hydroxylation at the 7- or 8- position. The dehydro-hydroxybrimonidine metabolites were characterized as 2-oxo or 3-oxo -4', 5'-dehydrobrimonidine. A novel metabolite ((4-bromo-lH-benzoimidazol-5-yl)-imidazolidin-2-ylidene-amine) of benzimidazole derivative of brimonidine in rats in vivo was identified and confirmed with reference standard. In conclusion, on-line H/D exchange LC-MS/MS and stable-isotope tracer techniques are useful for the characterization of brimonid...